This invention relates generally to a test apparatus for measuring surface runoff water infiltration into a manhole and specifically to an apparatus used to simulate and measure the infiltration inflow rate of surface runoff water (or other liquids) into one covered manhole and its surrounding support structure on site.
Surface water, caused usually by rain fall, infiltrates sanitary sewer systems which greatly increases the treatment volume demands on municipal sewage treatment systems. If surface water runoff is allowed to infiltrate into a sewer system, the overall volume of sewage treatment increases and therefore costs increase greatly in areas where there are large annual rain falls and commensurate infiltration. The unnecessary treatment of surface runoff water often can overwhelm a sewer plant capacity which itself then causes overflows of unprocessed sewage into streams and other bodies of water, damaging the environment.
In the past it has been difficult to quantitatively determine the additional water volume due to infiltration that is added to an entire sewer system caused by surface runoff resulting from runoff inflow into each single manhole and its supporting structure. Because manhole covers and their supporting structures are not identical, the infiltration inflow rates can be different at each manhole site. At the present time it is difficult to identify which particular manholes in a sewer system are responsible for high or unacceptable infiltration inflow rates.
The present invention provides a portable, low cost test device that can be employed on site at any manhole to determine the rate of volume of water flow as a function of time that can infiltrate through the manhole cover and its supporrrng surface.
Manhole covers allow surface water to enter sanitary sewers during rain fall because each manhole cover includes required vent holes to prevent gas build-up in the sewer line and pick holes to allow for removal of the manhole cover. Often a loose fit exists between the manhole supporting structure and the manhole cover which provides for runoff water inflow areas.
The prior art shows a device that has been used to measure waste water volumes within sewer systems in U.S. Pat. No. 4,367,652 issued to Venuso Jan. 11, 1983. A device for measuring liquid flow rates within a sewer system is shown in U.S. Pat. No. 4,669,308 issued to Joritsma on June 2, 1987. These devices do not provide for the test measurement of the surface water infiltration inflow rate about a manhole (cover and supporting equipment) but measure sewage flow rates within the sewer lines.
The present invention can provide objective, accurate evidence of the overall infiltration inflow rate of surface water into a sewer system to those who deal with runoff drainage problems or sanitary sewage systems.
The information that can be obtained from Applicant's invention will allow a corporate utility that is responsible for a sewage treatment plant to determine cost effective solutions for installing surface water diversion equipment available in the marketplace on predetermined manhole covers. With the use of an infiltration inflow test apparatus, the need for installing manhole diverter equipment at every manhole in a sewer system is eliminated. The test apparatus can identify those manhole structures with high inflow infiltration that need the installation of surface water diverter equipment and identify those manhole covers that do not need diverter equipment, greatly reducing diversion equipment installation and maintenance costs for the sewer utility.
It is essential that the test equipment not influence the test results and that the test environment most naturally simulates those conditions that exist when surface runoff water accumulates by rain fall at and over the manhole cover. While in operation, the present invention does not disturb the manhole cover or its supporting equipment but interacts with the manhole cover and support structure as normally in place, thereby providing realistic, accurate test measurements on site without any change of the manhole or its surroundings during the test.